1. Field of the Invention
The present invention relates to gas-insulated switchgear apparatus (hereinafter simply referred to as a GIS), and more particularly to a GIS of a construction in which a plurality of main buses are connected to a gas circuit breaker of the unsegregated three-phase type.
2. Description of the Prior Art
In a known type of GIS, a circuit breaker of the unsegregated three-phase type is used which is constructed so that the breakers of three phases are arranged in a sealed cylindrical enclosure along its axial direction so as to be positioned at the apexes of an equilateral or isosceles triangle. Then, the breaker of each phase is used in such a manner that one end is connected to one or more main buses the other end is connected to an outlet terminal such as a cable head or a main bus having bus conductors disposed in a ground housing in which an insulating gas is sealed.
Usually, the main buses and outlet terminals of this type of GIS are connected through a vertical-type sealed enclosure which is provided with openings formed in sides thereof having connecting flanges to which are attached insulating spacers having current carrying conductors embedded therein. An insulating gas such as SF.sub.6 is sealed in the enclosure and the enclosure is hermetically sealed. Where a plurality of main buses are connected to one side of such a sealed enclosure, each of the main buses is connected by a separate connecting flange disposed in the longitudinal direction of the enclosure and common conductors are arranged along breakers within the sealed enclosure to connect each of the main buses with one end of each of the breakers through the common conductors (see JP-A- No. 60-183910).
In the case of a type of GIS which monitors the conditions on the cable head side, the monitoring is effected by fitting a current transformer on the vertical connecting conductor from each breaker within a sealed enclosure (see JP-A- No. 60-183908). Also, in the case of another type of GIS which monitors the conditions on both the cable head side and the main bus side, the monitoring is effected by fitting a current transformer on the connecting conductor connected to each end of each breaker thereby arranging the current transformers in the upper and lower parts of a sealed enclosure or alternatively the monitoring is effected by arranging the current transformers on the sealed enclosure side of the connecting flanges (see JP-A-No. 60-213208 and JP-U-No. 62-98410). These constructions are the same with a bus connecting GIS for interconnecting main buses.
Thus, due to the arrangement of breakers of respective phases, common conductors, e.g., connecting conductors for connecting the breakers to main buses, current transformers, etc., within a sealed enclosure as mentioned above, the above-described conventional types of GIS are disadvantageous in that the insulating distance between these components, particularly the connecting conductors on the main bus side, must be ensured thus requiring an increase in the diameter of the sealed enclosure to increase the accommodating space and, thereby increasing the size of the GIS on the whole. Also, in the case of the construction in which the transformers of each phase are fitted on the connecting conductors from the ends of each breaker thereby arranging the current transformers above and below the breakers, not only the height dimension of the sealed enclosure is increased but also a measure must be taken to prevent the effects of high temperature gas due to the extinguishing of an arc during the operation of the breakers. Further, in the case of the construction where the current transformers are arranged with the connecting flange portions provided in the sealed enclosure, the size of the apparatus of the multiple main bus construction on the whole must be increased in consideration of the required accommodating space.